Conventionally, an air conditioner for a hybrid vehicle determines whether or not it is necessary to heat the interior of the vehicle based on sensor signals or the like from an inside air temperature sensor and an outside air temperature sensor, even when the temperature of coolant of an engine detected by a water temperature sensor is low. When the heating of the vehicle interior is determined to be necessary, the engine is operated even in an operation state of the hybrid vehicle at startup or during a low-speed vehicle running. Therefore, the coolant can be sufficiently warmed in a water jacket of the engine, and the warmed water is supplied to a heater core so as to heat the vehicle interior (see, for example, JP-A-10-278569).
In the above air conditioner, when the heating of the vehicle interior is determined to be necessary, the engine is operated to ensure a heating capacity in the air conditioner. However, in this case, fuel efficiency in the engine is deteriorated.